all the versions of Eagle I've worked with keep the regular resistors in rcl.lbr ... I've never seen r.lbr!
so if you want round pads, then copy rcl.lbr to a different directoy (outside eagle), and name it something like rcl-roundpads
now open that library, and edit the parts you need to have round pads
save your changes, and go into your schematic
type this command
UPDATE rcl = c:\newlbr\rcl-roundpads.lbr;
the semicolon is important, it tells eagle to check all parts
this will replace any and all parts in the old rcl library with parts from the new library
alternately, you can also do a CHANGE PACKAGE and specifiy a different package from a new library, but I can't remember the exact syntax for that.